The present invention pertains to a sewing or embroidery machine.
Prior-art sewing machines have, in general, a hook cooperating with a thread-carrying needle as well as a feed device with a drive for the feed element and a holding-down means with a presser foot for the fabric being sewn.
During the sewing operation, the fabric being sewn is usually held between the feed element and the presser foot, which lies on the fabric being sewn in a non-positive manner. The feed element, which is usually driven in a positive-locking manner and is provided with teeth on its top side, moves forward out of the area of the needle plate during the feed phase proper and presses the fabric to be sewn against the presser foot and it pushes the presser foot upward. The feed element now performs an essentially elliptical movement, and the feed movement proper takes place in the direction of the longitudinal axis of the ellipse and the lifting movement in the direction of the minor axis of the ellipse.
If these movements are brought about by means of mechanical gears, cam or control lever mechanisms are usually used for this purpose, and the stitch length can be changed by displacing the articulation points in the case of control lever mechanisms and either by changing the effective eccentricity of the cam or by changing the oblique position of the corresponding crank in the case of cam mechanisms. Thus, while the stitch length can be changed during sewing by actuating a manual button or another actuating means, the lifting movement of the feeder can be changed by an intervention performed by means of tools only when the machine has been stopped.
It has become known from DE 29 03 031 in connection with pattern-forming zigzag sewing machines that the feeder can be moved by means of an impulse motor via linkages and lever mechanisms in order to thus bring about a change in the length of the corresponding sewing pattern by changing the stitch length. To make it possible to change the width of the sewing pattern during sewing as well, the drive generating the transverse movement of the needle bar also has an impulse motor, by means of which the overstitch width of the needle movement can be changed.
Even though it is thus known that both the overstitch width of the needle movement and the stitch length can be changed during sewing, also changing the amount of the vertical movement of the feed element during sewing has not become known since.
In prior-art sewing machines, the feed element strikes the presser foot in a rapid sequence during sewing, and the force with which the spring presses down the presser foot is selected to be relatively strong in order to prevent the presser foot from being lifted off from the fabric being sewn.
However, a temporary separation of the presser foot from the fabric being sewn cannot always be prevented even in the case of a relatively strong pressing force of the presser foot, which is on the order of magnitude of more than 6 kg, especially at high speeds of sewing, at which the forcibly driven feed element strikes the underside of the presser foot in a correspondingly rapid sequence and the presser foot is set to vibrate. This results, on the one hand, in a non-uniform feed of the fabric being sewn and, on the other hand, in an adverse effect on the quality of sewing due to the resulting non-uniform tapering of the stitch.
DE 36 36 548 A1 describes a sewing machine in which the presser foot for the fabric being sewn can be raised by means of a servo coil. The pressing force of the presser foot on the fabric being sewn can be set by means of another servo coil. Furthermore, the stitch length can be preset here manually and can be reduced by means of a servo magnet.
The values of the pressing force of the presser foot, which are read into a memory via a potentiometer, can be compared with preset values during the operation of the sewing machine, so that the pressing force of the presser foot on the fabric being sewn can be changed correspondingly. A dependence of the pressing force of the presser foot on the movement characteristic of the feed element is not intended here and is not achieved, either.
The basic object of the present invention is to provide a feed means for sewing machines of this class, which makes it possible, while guaranteeing a corresponding synchronization of the horizontal and vertical movements of the feed elements, to vary these [movements] independently from one another during sewing even at high speeds of rotation.
This object is accomplished in a sewing machine of this class by the feed means for driving the feed element having a linear drive with two drivable elements (rotors), wherein one rotor is movable in the horizontal direction and the other rotor in the vertical direction, and that a control means with a control circuit for the horizontal movements as well as with a control circuit for the vertical movements of the feed element is associated with the feed means, wherein both control circuits are subordinated to a main control means, which has a data processing means and receives its synchronization impulses from an encoder as a function of the particular instantaneous position of the needle or hook, and to which the actual values of the horizontal and/or vertical movements of the feed element can be alternatingly sent.
This offers the possibility of changing both the amount and the phase position of the vertical movement of the feed element independently from both the amount and the phase position of its horizontal movement and of affecting the amount of the vertical movement of the feed element independently from its horizontal movement such that a sufficient flux of force is guaranteed between the fabric being sewn and the feed element, on the one hand, and, on the other hand, it is not necessary to select a needlessly strong contact pressure of the presser foot. It is, of course, also possible to vary the phase position of the vertical movement and/or the phase position of the horizontal movement of the feed element within limits preset by the requirements of stitch formation in relation to the phase position of the movement of the needle and/or hook.
While the intervention with the movement characteristic of the feed element is performed exclusively to change the stitch length in the prior art, intervention in the characteristic of the vertical and/or horizontal movement of the feed element is possible according to the present invention at any time due to the main control means (even while the stitch length is maintained) during each and every stitch formation operation In order to always perform the entire phase of stitch formation while maintaining optimal conditions.
All the mechanical components, such as shafts and gear trains, which are needed in prior-art sewing machines to move the feed element and to change its movement, may be eliminated due to the present invention, and so are, in particular, the electromechanical auxiliary units which are known in sewing machines with automatically adjustable stitch length and sewing direction as well. The stitch length and the sewing direction can be changed at full sewing speed.
Another object of the present invention is to provide feed and holding-down means for a sewing machine of this class, which make it possible to affect the cooperation of the presser foot with the feed element such that the pressing force of the presser foot can be adjusted during the sewing operation to the particular instantaneous velocity and the instantaneous vertical force of the feed element.
This object is accomplished in sewing machines of this class by the cooperation of the feed element with the presser foot being able to be regulated by a main control means having a data processing means and acting on both a control means for the drive of the feed element and on a control means for the drive of the presser foot such that the pressing force of the presser foot follows the instantaneous movement of the feed element, wherein the main control means receives its synchronization from an encoder as a function of the particular instantaneous position of the needle or hook.
The pressing force of the presser foot can be adjusted by the main control means to the movement characteristic of the feed element during every individual feed step of the feed element and consequently during the entire stitch formation operation in this case as well. Since the pressing force of the presser foot can be adjusted to the particular instantaneous velocity of the feed element correctly for the particular stitch for the entire sewing operation, an optimal cooperation between the presser foot and the feed element and consequently a considerable improvement of the quality of sewing are achieved while both the noise level and the vibrations of the sewing machine are reduced at the same time.
An embodiment that is favorable in terms of control engineering is obtained by the actual values of the vertical movements and/or the horizontal movements of the feed element, but especially the actual values of the vertical movements being able to be sent to the main control means, and by the control of the drive for the presser foot being performed as a function of the actual values of the feed element, especially the actual values of the vertical movement of the feed element.
To make it possible to move the presser foot rapidly into its two end positions or into its working position at both the beginning and the end of the sewing and optionally also during interruptions in sewing, the presser foot can be moved alternatingly into its upper or lower end position by means of external signals that can be sent to its drive. The presser foot can thus be moved rapidly into its end positions or into its working position, in which it will apply a pressing force on the fabric being sewn, which force is adjusted to the movement characteristic of the horizontal or vertical movement of the feed element.
The mechanical components such as leaf springs, bowden cable, toggle levers and the magnet of the presser foot, which are needed for actuating the presser foot, are eliminated by the present invention.
Based on the horizontal and vertical movements of the feed element being controlled independently from one another and due to the changing of the vertical and/or horizontal movements of the feed element, the present invention offers the possibility of also using the feed element at the same time as a carrier bracket for a catch thread device/thread cutter to be fastened thereto and of moving this [the feed element] together with the catch thread device/thread cutter such that the bobbin thread and the leg of the needle thread loop to be caught can be caught by the catch thread device/thread cutter and fed to a cutter during an increased horizontal movement and optionally also an increased vertical movement of the feed element, which can be initiated by an external signal that can be sent to the drive of the feed means. Compared with the prior-art thread-cutting system, this leads to a substantial reduction in the effort needed for catching needle and bobbin threads and the cutting operation can take place at a higher sewing speed.
According to another suggestion according to the present invention, the external signal that can be sent to the drive of the feed means for increasing the movement of the feed element may also be used to release the tensioning means for the needle thread.
If the catch thread device has caught the leg of the needle thread loop leading to the fabric being sewn, an optimally short end of the needle thread remaining on the fabric being sewn and a free length of the needle thread remaining on the thread reserve which guarantees reliable resewing can be obtained as a result.
To make it possible to store and poll various sewing and fabric parameters, such as the stitch length, feed velocity, pressing force of the presser foot as well as structure, thickness or surface finish of the fabric, as well as auxiliary functions, such as the raising and lowering of the presser foot or thread cutting, the data processing means has a memory for various sewing parameters and auxiliary functions, which can be polled by means of a control panel or an interface and can be sent to the main control means.
A quickly responding drive for the holding-down means can be obtained by designing this drive as an electronically controlled, electromagnetic single-axis linear drive, whose rotor is directly connected to the carrier bracket for the presser foot.
A quickly responding drive for the feed means can also be obtained by designing the electromagnetic linear drives of the feed means as a biaxial linear drive with two rotors that are connected to one another in terms of movement, one rotor being able to be driven in the horizontal direction and the other rotor in the vertical direction.
The movement of the rotor for the horizontal movement of the feed element may be able to be controlled in this case independently or depending on the movement of the rotor for the vertical movement of the feed element.
In a solution of simple design, the two rotors of the biaxial linear drive are integrated in one rotor, which can be driven in both the horizontal and vertical directions.
A solution in which only weak inertia forces are to be overcome for the movement of the feed element is obtained by the feed element being directly connected to one rotor or both rotors for its vertical and horizontal movement.
To make it possible to use the stator at the same time as a guide for the rotor and to accommodate at the same time a sufficient magnetic mass in the air gap, the rotors of the biaxial linear drive have a prismatic design and comprise polarized permanent magnets without iron short-circuit, as a result of which a favorable force-to-mass ratio of the magnetic material is obtained. These advantages are also achieved in the same manner in the case of the use of a prismatic rotor for the drive of the presser foot.
A solution that is characterized by wear resistance for high load cycles is obtained if the linear drives are designed as brushless linear drives.
To determine the particular instantaneous position of the feed element and of the presser foot, it is advantageous to connect the rotors of the linear drives indirectly or directly with a respective encoder, wherein the encoders for the horizontal and vertical movement of the feed element are integrated in a two-dimensional encoder, to which two mutually independent evaluating means are assigned.
The encoder disk advantageously has two groups of line elements, of which the first group extends in a first direction and can be scanned by the first evaluating means, while the second group extends in a second direction and can be scanned by the second evaluating means.